引言
之前Spring 一直用的xml配置文件比较多，现在发现新公司用的注解比较多。也就是通过定义一个配置类(以@Configuration注解的类)内部在方法上注解 @Bean 注解来完成Bean的依赖注入Spring容器。用注解来配置的话，其实就是减少了配置文件的工作，但总体来说代码可读性其实是会下降的。不过也省去了一大堆的xml配置文件
直接看源码
下面就从源码层面来看看 通过注解配置有什么不同
之前有分析过Spring对Bean的解析，是通过把我们配置的Bean信息抽象成了一个BeanDefiniion对象。这个对象持有了我们配置的Bean的元数据
那么其实 @Bean 的注解的原理也是类似，也是通过将我们配置的Bean信息抽象成一个BeanDefiniion对象
这里我们分两种情况讨论，一种是 Spring 通过 xml文件配置实现注解配置，一种就是我们现在非常流行的 SpringBoot实现的注解配置。其实两者实现原理一致，只是配置入口略有不同。
先看 普通 Spring 应用的配置:
如果我们要在 普通 Spring 应用中实现注解配置。那么我们需要在Spring的配置文件中配置以下几个配置
<context:annotation-config>
<context:component-scan>
这两个配置的意思是什么呢？
我们直接看Spring是如何解析这两个标签的吧，通过在META-INF/spring.handlers目录下根据spring.handlers文件可以找到 Context 标签 解析入口类 ContextNamespaceHandler
public class ContextNamespaceHandler extends NamespaceHandlerSupport {
@Override
public void init() {
registerBeanDefinitionParser("property-placeholder", new PropertyPlaceholderBeanDefinitionParser());
registerBeanDefinitionParser("property-override", new PropertyOverrideBeanDefinitionParser());
registerBeanDefinitionParser("annotation-config", new AnnotationConfigBeanDefinitionParser());
registerBeanDefinitionParser("component-scan", new ComponentScanBeanDefinitionParser());
registerBeanDefinitionParser("load-time-weaver", new LoadTimeWeaverBeanDefinitionParser());
registerBeanDefinitionParser("spring-configured", new SpringConfiguredBeanDefinitionParser());
registerBeanDefinitionParser("mbean-export", new MBeanExportBeanDefinitionParser());
registerBeanDefinitionParser("mbean-server", new MBeanServerBeanDefinitionParser());
}
}
看了上面的解析源码，可以知道annotation-config由AnnotationConfigBeanDefinitionParser解析。component-scan由ComponentScanBeanDefinitionParser解析。这里就是Spring XML 注解配置的入口，下面我们来依次分析这两个解析类干了什么事情？
- ComponentScanBeanDefinitionParser
public BeanDefinition parse(Element element, ParserContext parserContext) {
String basePackage = element.getAttribute(BASE_PACKAGE_ATTRIBUTE);
basePackage = parserContext.getReaderContext().getEnvironment().resolvePlaceholders(basePackage);
String[] basePackages = StringUtils.tokenizeToStringArray(basePackage,
ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
// Actually scan for bean definitions and register them.
ClassPathBeanDefinitionScanner scanner = configureScanner(parserContext, element);
// 这里扫描了我们配置的 base-package 包下全部 beanDefinitions，并抽象成了 BeanDefinitionHolder类
Set<BeanDefinitionHolder> beanDefinitions = scanner.doScan(basePackages);
// 将抽象的 beanDefinitions 全部注册进 Spring容器中，注 这里包含了被@Configuration注解的类
registerComponents(parserContext.getReaderContext(), beanDefinitions, element);
return null;
}
- AnnotationConfigBeanDefinitionParser
主要逻辑在 AnnotationConfigUtils 工具类的 registerAnnotationConfigProcessors方法中
public BeanDefinition parse(Element element, ParserContext parserContext) {
Object source = parserContext.extractSource(element);
// 初始化一些 BeanFactoryPostProcessor 进Spring容器，会在getBean之前全部执行。
// 一般用来在容器实例化Bean前，对BeanDefinition做修改，或添加新的BeanDefinition等前置修改
// 主要逻辑就在这里
Set<BeanDefinitionHolder> processorDefinitions =
AnnotationConfigUtils.registerAnnotationConfigProcessors(parserContext.getRegistry(), source);
// Register component for the surrounding <context:annotation-config> element.
CompositeComponentDefinition compDefinition = new CompositeComponentDefinition(element.getTagName(), source);
parserContext.pushContainingComponent(compDefinition);
// Nest the concrete beans in the surrounding component.
for (BeanDefinitionHolder processorDefinition : processorDefinitions) {
parserContext.registerComponent(new BeanComponentDefinition(processorDefinition));
}
// Finally register the composite component.
parserContext.popAndRegisterContainingComponent();
return null;
}
// AnnotationConfigUtils.class
// 添加支持 annotation-config 配置的一些BeanFactoryPostProcessor 实现类
public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(
BeanDefinitionRegistry registry, @Nullable Object source) {
DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);
if (beanFactory != null) {
if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {
beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);
}
if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {
beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());
}
}
Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<>(8);
// @Configuration 注解解析
if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
}
// @Autowired 注解解析
if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
}
// @Required 注解解析
if (!registry.containsBeanDefinition(REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(RequiredAnnotationBeanPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
}
// Check for JSR-250 support, and if present add the CommonAnnotationBeanPostProcessor.
// 对 JSR-250做支持 解析注解 @Resource @PostConstruct @PreDestroy
if (jsr250Present && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));
}
// Check for JPA support, and if present add the PersistenceAnnotationBeanPostProcessor.
if (jpaPresent && !registry.containsBeanDefinition(PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition();
try {
def.setBeanClass(ClassUtils.forName(PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME,
AnnotationConfigUtils.class.getClassLoader()));
}
catch (ClassNotFoundException ex) {
throw new IllegalStateException(
"Cannot load optional framework class: " + PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME, ex);
}
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME));
}
if (!registry.containsBeanDefinition(EVENT_LISTENER_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(EventListenerMethodProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_PROCESSOR_BEAN_NAME));
}
if (!registry.containsBeanDefinition(EVENT_LISTENER_FACTORY_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(DefaultEventListenerFactory.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_FACTORY_BEAN_NAME));
}
return beanDefs;
}
可以看到 annotation-config 配置其实就是添加了几个 BeanFactoryPostProcessor 实现类，以此来实现 Autowired Configuration @Resource @PostConstruct @PreDestroy 等注解的实现。其他的注解暂且不看，我们直接看今天的重点 Configuration 注解是如何解析，@Configuration是通过 BeanFactoryPostProcessor 的实现类 ConfigurationClassPostProcessor 类在Spring启动的时候执行的（具体BeanFactoryPostProcessor的执行时机可以看我另一篇博文链接)
- ConfigurationClassPostProcessor
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
int registryId = System.identityHashCode(registry);
// 判断是否已经执行过
if (this.registriesPostProcessed.contains(registryId)) {
throw new IllegalStateException(
"postProcessBeanDefinitionRegistry already called on this post-processor against " + registry);
}
if (this.factoriesPostProcessed.contains(registryId)) {
throw new IllegalStateException(
"postProcessBeanFactory already called on this post-processor against " + registry);
}
this.registriesPostProcessed.add(registryId);
// 正式执行逻辑
processConfigBeanDefinitions(registry);
}
public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
List<BeanDefinitionHolder> configCandidates = new ArrayList<>();
String[] candidateNames = registry.getBeanDefinitionNames();
// 遍历所有 BeanDefinition name
for (String beanName : candidateNames) {
BeanDefinition beanDef = registry.getBeanDefinition(beanName);
// 判断是否已经处理过
if (ConfigurationClassUtils.isFullConfigurationClass(beanDef) ||
ConfigurationClassUtils.isLiteConfigurationClass(beanDef)) {
if (logger.isDebugEnabled()) {
logger.debug("Bean definition has already been processed as a configuration class: " + beanDef);
}
}
// 条件筛选
else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) {
configCandidates.add(new BeanDefinitionHolder(beanDef, beanName));
}
}
// 栓选完为空 直接返回
if (configCandidates.isEmpty()) {
return;
}
// 根据 @Order 注解排序
configCandidates.sort((bd1, bd2) -> {
int i1 = ConfigurationClassUtils.getOrder(bd1.getBeanDefinition());
int i2 = ConfigurationClassUtils.getOrder(bd2.getBeanDefinition());
return Integer.compare(i1, i2);
});
// Detect any custom bean name generation strategy supplied through the enclosing application context
// 获取 BeanName 生成策略
SingletonBeanRegistry sbr = null;
if (registry instanceof SingletonBeanRegistry) {
sbr = (SingletonBeanRegistry) registry;
if (!this.localBeanNameGeneratorSet) {
BeanNameGenerator generator = (BeanNameGenerator) sbr.getSingleton(CONFIGURATION_BEAN_NAME_GENERATOR);
if (generator != null) {
this.componentScanBeanNameGenerator = generator;
this.importBeanNameGenerator = generator;
}
}
}
if (this.environment == null) {
this.environment = new StandardEnvironment();
}
// Parse each @Configuration class
// 解析 @Configuration 注解
ConfigurationClassParser parser = new ConfigurationClassParser(
this.metadataReaderFactory, this.problemReporter, this.environment,
this.resourceLoader, this.componentScanBeanNameGenerator, registry);
Set<BeanDefinitionHolder> candidates = new LinkedHashSet<>(configCandidates);
Set<ConfigurationClass> alreadyParsed = new HashSet<>(configCandidates.size());
do {
parser.parse(candidates);
parser.validate();
Set<ConfigurationClass> configClasses = new LinkedHashSet<>(parser.getConfigurationClasses());
configClasses.removeAll(alreadyParsed);
// Read the model and create bean definitions based on its content
// 读取并解析注册 BeanDefinition
if (this.reader == null) {
this.reader = new ConfigurationClassBeanDefinitionReader(
registry, this.sourceExtractor, this.resourceLoader, this.environment,
this.importBeanNameGenerator, parser.getImportRegistry());
}
this.reader.loadBeanDefinitions(configClasses);
alreadyParsed.addAll(configClasses);
candidates.clear();
// 处理新加入的
if (registry.getBeanDefinitionCount() > candidateNames.length) {
String[] newCandidateNames = registry.getBeanDefinitionNames();
Set<String> oldCandidateNames = new HashSet<>(Arrays.asList(candidateNames));
Set<String> alreadyParsedClasses = new HashSet<>();
for (ConfigurationClass configurationClass : alreadyParsed) {
alreadyParsedClasses.add(configurationClass.getMetadata().getClassName());
}
for (String candidateName : newCandidateNames) {
if (!oldCandidateNames.contains(candidateName)) {
BeanDefinition bd = registry.getBeanDefinition(candidateName);
if (ConfigurationClassUtils.checkConfigurationClassCandidate(bd, this.metadataReaderFactory) &&
!alreadyParsedClasses.contains(bd.getBeanClassName())) {
candidates.add(new BeanDefinitionHolder(bd, candidateName));
}
}
}
candidateNames = newCandidateNames;
}
}
while (!candidates.isEmpty());
// Register the ImportRegistry as a bean in order to support ImportAware @Configuration classes
if (sbr != null && !sbr.containsSingleton(IMPORT_REGISTRY_BEAN_NAME)) {
sbr.registerSingleton(IMPORT_REGISTRY_BEAN_NAME, parser.getImportRegistry());
}
if (this.metadataReaderFactory instanceof CachingMetadataReaderFactory) {
// Clear cache in externally provided MetadataReaderFactory; this is a no-op
// for a shared cache since it'll be cleared by the ApplicationContext.
((CachingMetadataReaderFactory) this.metadataReaderFactory).clearCache();
}
}
具体的执行逻辑在ConfigurationClassParser 类的 parse 方法中
- ConfigurationClassParser
核心解析方法是 doProcessConfigurationClass方法，下面直接看这个方法的实现
protected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass)
throws IOException {
// Recursively process any member (nested) classes first
processMemberClasses(configClass, sourceClass);
// Process any @PropertySource annotations
// 解析 @PropertySource
for (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable(
sourceClass.getMetadata(), PropertySources.class,
org.springframework.context.annotation.PropertySource.class)) {
if (this.environment instanceof ConfigurableEnvironment) {
processPropertySource(propertySource);
}
else {
logger.warn("Ignoring @PropertySource annotation on [" + sourceClass.getMetadata().getClassName() +
"]. Reason: Environment must implement ConfigurableEnvironment");
}
}
// Process any @ComponentScan annotations
// 解析 @ComponentScan
Set<AnnotationAttributes> componentScans = AnnotationConfigUtils.attributesForRepeatable(
sourceClass.getMetadata(), ComponentScans.class, ComponentScan.class);
if (!componentScans.isEmpty() &&
!this.conditionEvaluator.shouldSkip(sourceClass.getMetadata(), ConfigurationPhase.REGISTER_BEAN)) {
for (AnnotationAttributes componentScan : componentScans) {
// The config class is annotated with @ComponentScan -> perform the scan immediately
Set<BeanDefinitionHolder> scannedBeanDefinitions =
this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());
// Check the set of scanned definitions for any further config classes and parse recursively if needed
for (BeanDefinitionHolder holder : scannedBeanDefinitions) {
BeanDefinition bdCand = holder.getBeanDefinition().getOriginatingBeanDefinition();
if (bdCand == null) {
bdCand = holder.getBeanDefinition();
}
if (ConfigurationClassUtils.checkConfigurationClassCandidate(bdCand, this.metadataReaderFactory)) {
parse(bdCand.getBeanClassName(), holder.getBeanName());
}
}
}
}
// Process any @Import annotations
// 解析 @Import
processImports(configClass, sourceClass, getImports(sourceClass), true);
// Process any @ImportResource annotations
// 解析 @ImportResource
AnnotationAttributes importResource =
AnnotationConfigUtils.attributesFor(sourceClass.getMetadata(), ImportResource.class);
if (importResource != null) {
String[] resources = importResource.getStringArray("locations");
Class<? extends BeanDefinitionReader> readerClass = importResource.getClass("reader");
for (String resource : resources) {
String resolvedResource = this.environment.resolveRequiredPlaceholders(resource);
configClass.addImportedResource(resolvedResource, readerClass);
}
}
// Process individual @Bean methods
// 解析 @Bean
Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
for (MethodMetadata methodMetadata : beanMethods) {
configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
}
// Process default methods on interfaces
processInterfaces(configClass, sourceClass);
// Process superclass, if any
if (sourceClass.getMetadata().hasSuperClass()) {
String superclass = sourceClass.getMetadata().getSuperClassName();
if (superclass != null && !superclass.startsWith("java") &&
!this.knownSuperclasses.containsKey(superclass)) {
this.knownSuperclasses.put(superclass, configClass);
// Superclass found, return its annotation metadata and recurse
return sourceClass.getSuperClass();
}
}
// No superclass -> processing is complete
return null;
}
可以看到上面的代码依次解析了 @PropertySource，@ComponentScan @Bean @Import 等注解。这里我们重点关注 @Bean 的实现
// 获取 @bean 注解修饰的 方法元数据信息
Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
for (MethodMetadata methodMetadata : beanMethods) {
// 封装成 BeanMethod
configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
}
下面我们回到 ConfigurationClassPostProcessor ，解析完 元数据之后，就是加载注册 BeanDefinition了
this.reader.loadBeanDefinitions(configClasses);
public void loadBeanDefinitions(Set<ConfigurationClass> configurationModel) {
TrackedConditionEvaluator trackedConditionEvaluator = new TrackedConditionEvaluator();
for (ConfigurationClass configClass : configurationModel) {
loadBeanDefinitionsForConfigurationClass(configClass, trackedConditionEvaluator);
}
}
private void loadBeanDefinitionsForConfigurationClass(
ConfigurationClass configClass, TrackedConditionEvaluator trackedConditionEvaluator) {
if (trackedConditionEvaluator.shouldSkip(configClass)) {
String beanName = configClass.getBeanName();
if (StringUtils.hasLength(beanName) && this.registry.containsBeanDefinition(beanName)) {
this.registry.removeBeanDefinition(beanName);
}
this.importRegistry.removeImportingClass(configClass.getMetadata().getClassName());
return;
}
if (configClass.isImported()) {
registerBeanDefinitionForImportedConfigurationClass(configClass);
}
for (BeanMethod beanMethod : configClass.getBeanMethods()) {
// 解析之前 解析 @bean 加入的 beanMethod信息
loadBeanDefinitionsForBeanMethod(beanMethod);
}
loadBeanDefinitionsFromImportedResources(configClass.getImportedResources());
loadBeanDefinitionsFromRegistrars(configClass.getImportBeanDefinitionRegistrars());
}
看看 loadBeanDefinitionsForBeanMethod 方法的实现，其实就是从BeanMethod中提取信息组装成 BeanDefinition
private void loadBeanDefinitionsForBeanMethod(BeanMethod beanMethod) {
ConfigurationClass configClass = beanMethod.getConfigurationClass();
MethodMetadata metadata = beanMethod.getMetadata();
String methodName = metadata.getMethodName();
// 判断是否需要跳过
if (this.conditionEvaluator.shouldSkip(metadata, ConfigurationPhase.REGISTER_BEAN)) {
configClass.skippedBeanMethods.add(methodName);
return;
}
if (configClass.skippedBeanMethods.contains(methodName)) {
return;
}
AnnotationAttributes bean = AnnotationConfigUtils.attributesFor(metadata, Bean.class);
Assert.state(bean != null, "No @Bean annotation attributes");
// 考虑别名 名称
List<String> names = new ArrayList<>(Arrays.asList(bean.getStringArray("name")));
String beanName = (!names.isEmpty() ? names.remove(0) : methodName);
// 注册别名
for (String alias : names) {
this.registry.registerAlias(beanName, alias);
}
// Has this effectively been overridden before (e.g. via XML)?
// 判断是否在 xml配置文件中 已经配置过
if (isOverriddenByExistingDefinition(beanMethod, beanName)) {
if (beanName.equals(beanMethod.getConfigurationClass().getBeanName())) {
throw new BeanDefinitionStoreException(beanMethod.getConfigurationClass().getResource().getDescription(),
beanName, "Bean name derived from @Bean method '" + beanMethod.getMetadata().getMethodName() +
"' clashes with bean name for containing configuration class; please make those names unique!");
}
return;
}
ConfigurationClassBeanDefinition beanDef = new ConfigurationClassBeanDefinition(configClass, metadata);
beanDef.setResource(configClass.getResource());
beanDef.setSource(this.sourceExtractor.extractSource(metadata, configClass.getResource()));
// 这里可以知道 @bean 配置是 通过 FactoryMethod 来初始化的
if (metadata.isStatic()) {
// static @Bean method
beanDef.setBeanClassName(configClass.getMetadata().getClassName());
beanDef.setFactoryMethodName(methodName);
}
else {
// instance @Bean method
beanDef.setFactoryBeanName(configClass.getBeanName());
beanDef.setUniqueFactoryMethodName(methodName);
}
beanDef.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_CONSTRUCTOR);
beanDef.setAttribute(RequiredAnnotationBeanPostProcessor.SKIP_REQUIRED_CHECK_ATTRIBUTE, Boolean.TRUE);
AnnotationConfigUtils.processCommonDefinitionAnnotations(beanDef, metadata);
// 设置autowire属性
Autowire autowire = bean.getEnum("autowire");
if (autowire.isAutowire()) {
beanDef.setAutowireMode(autowire.value());
}
// 设置initMethod 初始化方法
String initMethodName = bean.getString("initMethod");
if (StringUtils.hasText(initMethodName)) {
beanDef.setInitMethodName(initMethodName);
}
// 设置destroyMethod 销毁方法
String destroyMethodName = bean.getString("destroyMethod");
beanDef.setDestroyMethodName(destroyMethodName);
// 获取 scope
ScopedProxyMode proxyMode = ScopedProxyMode.NO;
AnnotationAttributes attributes = AnnotationConfigUtils.attributesFor(metadata, Scope.class);
if (attributes != null) {
beanDef.setScope(attributes.getString("value"));
proxyMode = attributes.getEnum("proxyMode");
if (proxyMode == ScopedProxyMode.DEFAULT) {
proxyMode = ScopedProxyMode.NO;
}
}
// Replace the original bean definition with the target one, if necessary
// 如有必要，将原始Bean定义替换为目标Bean定义
BeanDefinition beanDefToRegister = beanDef;
if (proxyMode != ScopedProxyMode.NO) {
BeanDefinitionHolder proxyDef = ScopedProxyCreator.createScopedProxy(
new BeanDefinitionHolder(beanDef, beanName), this.registry,
proxyMode == ScopedProxyMode.TARGET_CLASS);
beanDefToRegister = new ConfigurationClassBeanDefinition(
(RootBeanDefinition) proxyDef.getBeanDefinition(), configClass, metadata);
}
if (logger.isDebugEnabled()) {
logger.debug(String.format("Registering bean definition for @Bean method %s.%s()",
configClass.getMetadata().getClassName(), beanName));
}
this.registry.registerBeanDefinition(beanName, beanDefToRegister);
}
代码解析到这里为止，@Bean配置的Bean信息就被全部抽象成了一个 BeanDefinition对象，接下来的Bean加载等等一大堆逻辑走的就是Spring的同一套逻辑了。
以上是通过在配置文件中配置 <context:annotation-config> <context:component-scan>。
Springboot怎么做的
那么Spring Boot并不需要配置文件，它又是在哪里配置了入口呢？
其实在之前的分析Spring boot的启动过程时 已经有提到了链接
，其实是在初始化 Spring容器的构造方法中进行了配置的加载，并且最终也是调用了 AnnotationConfigUtils 工具类的 registerAnnotationConfigProcessors方法
总结
终于写完了，其实分析来分析去，不论是Spring Boot Spring mvc 其实最核心不变的还是 Spring Framework，只要把核心搞清楚了，下次Spring 又推出什么 Spring xxx 也能应付自如
Spring 系列
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